This invention relates to the manufacture of springs, including the production of rod for making the springs, and more particularly to the manufacture of coiled springs, e.g., helically coiled springs or conical coiled springs, including the production of round steel rod for making the springs.
Reference is made herein to "rod" and "wire". These terms are used in the sense of their technical meaning in the metallurgical arts, namely, "rod" means rod formed by hot rolling, which may be drawn into wire, and "wire" means wire drawn from "rod".
The invention is especially concerned with the manufacture of springs which are cold wound. Where such springs of uniform pitch are required, they have heretofore generally been made from oil-tempered steel wire, which is wire formed by drawing hot rolled steel rod through a drawing die, and oil tempering the resultant wire. Oil tempering is a term of art identifying a process generally involving heating the wire to austenitizing temperatures, quenching it in oil, tempering it by reheating it, and recoiling it. Reference may be made to Chapter 5, entitled Oil Tempering, of the Steel Wire Handbook published in 1969 by The Wire Association, Inc. for a detailed description of the oil tempering of wire.
In the overall process such as heretofore employed, after the rod has been produced by hot rolling, it is cleaned with acid, coated with lime, pulled through a drawing die, coiled, uncoiled, then fed for oil tempering successively through a first heating means for austenitizing it, an oil bath for quenching it, and a second heating means for tempering it, then recoiled, and ultimately wound into springs. It has heretofore been regarded as essential to draw the rod into wire for forming springs because the rod has not been within the necessary limits of tolerance insofar as its gauge and roundness are concerned (it is generally "out-of-round" beyond the relatively close tolerance required for the winding of springs with uniform pitch), and also because the rod has not been sufficiently smooth.